As is well known, as a spark-ignition gasoline internal combustion engine, a so-called direct-injection (GDI) internal combustion engine is provided, which is aimed to improve fuel economy by lean burn and enhance output power by homogeneous combustion.
In such an engine, it is known that provision of a thermal insulating material partly in a crown surface of a piston made of aluminum alloy, wherein the crown surface forms a combustion chamber, produces an effect to promote atomization of injected fuel. However, it is difficult to tightly bind the thermal insulating material to the aluminum alloy base material.
Therefore, as described in a patent document 1 below, it is proposed to impregnate a porous thermal insulating material with an aluminum alloy base material, wherein the thermal insulating material is lower in thermal conductivity than the aluminum alloy base material, and thereby tightly bind the thermal insulating material to the aluminum alloy base material.